The present invention is related to variable valve train systems for use on internal combustion engines; more particularly, to devices for controllably varying the lift of valves in such engines; and most particularly, to a cam rocker (CR) variable valve train device that enables engine load control without a conventional throttle by varying the lift of the intake valves, the open valve duration, and the phasing of valve events relative to the motion of the engine""s pistons.
Internal combustion engine performance has progressed considerably in the past century. Inventions have yielded cleaner exhaust and enhanced durability, fuel efficiency, and power. Systems for varying the lift and timing of intake valves can further refine and enhance the performance of the internal combustion engine by controllably varying the volume of fuel mix supplied to the combustion chambers as a function of engine load and rotational speed. Fuel economy at part load operation can be increased by promoting more thorough combustion, reducing pumping work done by the pistons, which saps energy, deactivating cylinders, and/or by implementing a lean air/fuel ratio scheme. Matching the intake valve closing time more closely to the engine""s needs can enhance driveability of a vehicle by improving engine breathing at full engine load. Moreover, if intake and exhaust events can be controlled sufficiently to vary engine load, speed, and fuel dilution over the entire spectrum of required engine operating conditions, a controllable variable valve train can obviate the need for a throttle valve and EGR valve in a gas or diesel internal combustion engine.
A range of variable valve train devices and valve timing mechanisms for enhancing engine performance are known in the automotive art, but commercial use of such devices generally has been impractical because of cost, size, and/or operating limitations which have limited their true value and practicality. For example, a variable valve timing (VVT) mechanism as disclosed in U.S. Pat. No. 5,937,809 issued Aug. 17, 1999 to Pierik et al., employs a segmented single shaft crank rocker (SSCR) for operating individual or multiple engine valves by engaging a linkage with a rotary eccentric, preferably a rotary cam, to drive an oscillatable rocker cam. The SSCR mechanism disclosed in Pierik et al. has four moving components and thus can be expensive to manufacture and subject to wear and premature failure at a plurality of joints.
It is a principal object of the present invention to provide total authority over intake valve lift, open valve duration, and phasing of intake and exhaust events relative to the motion of an engine""s pistons.
It is a further object of the invention to improve peak engine torque and fuel economy.
It is a still further object of the invention to controllably vary the engine load directly at the engine cylinder, thereby eliminating the need for prior art throttle body and idle air control devices.
It is a still further object of the invention to reduce the size and number of components of the device in comparison with prior art variable valve train devices.
It is a still further object of the invention to provide a variable valve train device which can be economically mass-produced for commercial use in vehicles powered by internal combustion engines.
Briefly described, a cam rocker (CR) variable valve train device in accordance with the invention is provided for installation on an internal combustion engine having a rotary camshaft and a cam lobe fixed thereupon for rotation in timed relationship to the motion of the pistons of the engine. A close-fitting frame is rotationally disposed on the camshaft such that the camshaft is free to rotate within the frame. The frame is pivotably connected to an auxiliary control shaft such that the angular orientation of the frame may be controlled with respect to the camshaft. A rocker arm is pivotably disposed on the frame and is provided with an input roller which follows the lobe of the camshaft to correspondingly oscillate an output roller at the output end of the rocker in response to rotary motion of the cam. The output roller drives a cam spring cup rotatably disposed on the camshaft and attached to an output cam which cooperates with a cam follower to actuate the stem of an engine intake valve to open the valve conventionally against a valve spring. A curved return spring disposed between the spring cup and the frame is compressed by the valve-opening motion of the output cam and serves to return the cam to permit the valve to close. In a preferred embodiment for controlling the motion of two parallel valves at a single engine cylinder, the elements of the frame, cam spring cup, output cam, and spring are doubled symmetrically about the camshaft lobe and the rocker arm, the output roller cooperating with a bridge element connecting the two cam spring cups for simultaneous and identical actuation thereof. Rotation of the frame about the camshaft serves to alter the timing of the valve opening with respect to the associated piston, the height of the valve lift, and the duration of opening. Preferably, each cylinder in an internal combustion engine is provided with an apparatus in accordance with the present invention. The disclosed invention is thus capable of controlling engine load and peak engine torque directly at the cylinder head without resort to a conventional throttle and exhaust gas recirculation (EGR) valve.